1. Field of the Invention
The present invention relates to a bootstrap circuit for a voltage converter, and more particularly, to a bootstrap circuit for a voltage converter which can maintain a charge voltage for a bootstrap capacitor as well as detect a voltage value of the bootstrap capacitor.
2. Description of the Prior Art
Electronic devices usually have different composing elements which operate with different operational voltages. Thus, it is necessary to utilize different DC-DC voltage converters in order to achieve different voltage modulations, such as modulation for raising voltage values or degradation voltage values, and to maintain them at predetermined voltage values. Many types of DC-DC voltage converters have been widely developed and are derived from the buck/step down converter or the boost/step up converter. The buck converter can decrease an input DC voltage to a default voltage level, and the boost converter can increase the input DC voltage to another default voltage level. With development, both the buck and boost converters are varied and modified to conform to different system architectures and requirements.
Please refer to FIG. 1, which illustrates a conventional schematic diagram of a voltage converter 10. As shown in FIG. 1, the voltage converter 10 includes a driver 100, a bootstrap circuit 102, a switch element SWM, an inductor L1, a bootstrap capacitor CBOOT, a diode D1 and an output capacitor COUT. The driver 100 controls a conduction condition of the switch element SWM, so as to utilize the bootstrap circuit 102 to control a charge condition of the bootstrap capacitor CBOOT, i.e. voltage differences between two terminal points BOOT and LX. Lastly, the diode D1 and the output capacitor COUT stably transform an input voltage VIN into an output voltage VOUT for outputting. However, during the transformation process, the terminal point LX may possibly generate a relatively negative voltage value, so as to meet difficulty in voltage modulation of the bootstrap circuit 102, or to damage the bootstrap capacitor CBOOT. Besides, a period corresponding to voltage changes of the terminal point LX can be extremely short, and the bootstrap circuit 102 may not immediately output a control signal (not shown in figure) to control the charge condition of the bootstrap capacitor CBOOT.
Therefore, it has become an important issue to provide another bootstrap circuit for the voltage converter, so as to control the terminal voltage value of the bootstrap capacitor and the conduction condition thereof.